When the patient is asked to look upwards with the head fixed, there will be absence of wrinkling on the forehead, this is known as:
First, I need to recall clinical signs associated with facial nerve palsy. The frontal branch of the facial nerve (CN VII) innervates the frontalis muscle, which is responsible for raising the eyebrows and creating forehead wrinkles. If the patient can't wrinkle their forehead when looking up, it suggests a problem with the frontalis muscle, pointing to a lower motor neuron lesion of the facial nerve.
The key here is differentiating between upper and lower motor neuron lesions. Upper motor neuron lesions (like a stroke) would spare the forehead because the upper face is bilaterally innervated. So, if the forehead isn't moving, it's a lower motor neuron issue. The sign described is called the "forehead sign" or "loss of the forehead fold on upward gaze," which is specific for facial nerve palsy, not a central lesion.
The options probably include terms like Bell's sign, Marcus Gunn sign, etc. Bell's sign refers to the inability to close the eye fully during facial palsy. Marcus Gunn is associated with ptosis and jaw movement. So the correct answer here would be the absence of forehead wrinkling indicating facial nerve damage, which is a key differentiator from central causes like stroke.
Therefore, the correct answer is likely an option that mentions facial nerve palsy or lower motor neuron lesion. The distractors would be other signs related to different conditions. The clinical pearl is that central lesions spare the forehead, while peripheral lesions do not.
**Core Concept**
This question tests the understanding of facial nerve (CN VII) function, specifically the role of the frontalis muscle innervated by the frontal branch. Absence of forehead wrinkling during upward gaze indicates a lower motor neuron lesion affecting the facial nerve.
**Why the Correct Answer is Right**
The frontalis muscle is exclusively innervated by the facial nerve’s frontal branch. When the head is fixed, upward gaze causes the frontalis to contract, creating forehead wrinkles. Failure to do so suggests a peripheral facial nerve palsy (e.g., Bell’s palsy), as central lesions (e.g., stroke) spare the forehead due to bilateral cortical control of the upper face.
**Why Each Wrong Option is Incorrect**
**Option A:** (e.g., Marcus Gunn sign) Incorrect. This refers to jaw movement causing ptosis in Horner’s syndrome, unrelated to facial nerve function.
**Option B:** (e.g., Bell’s sign) Incorrect. Bell’s sign describes inability to close the eye fully during facial palsy, not forehead movement.
**Option C:** (e.g., Central facial palsy) Incorrect. Central lesions spare forehead movement due to bilateral upper motor neuron innervation.
**Clinical Pearl / High-Yield Fact**
Central vs. peripheral facial palsy: **Forehead sparing** in central lesions (stroke) is critical. Always test forehead wrinkling to localize the lesion. A peripheral lesion (Bell’s palsy) causes complete hemifacial weakness, including the